1. Field of the Invention
The present invention relates to a transflective type liquid crystal display device and a manufacturing method thereof.
2. Description of Related Art
In general, a liquid crystal display device is classified into two types, i.e., a transmissive type and a reflective type. The transmissive type liquid crystal display device displays an image by using a backlight placed on the back surface side. The reflective type liquid crystal display device displays an image by using a reflective plate placed on the substrate and reflecting ambient light on the surface of the reflective plate. The transmissive liquid crystal display device has a disadvantage that when ambient light is very bright, such as direct sunlight, it is difficult to view the display since display light is darker than the ambient light. On the other hand, the reflective liquid crystal display device has a disadvantage that visibility decreases significantly when ambient light is dark.
In order to compensate these disadvantages, there is proposed a transflective type liquid crystal display device which has both a transmission mode of transmitting a part of light and a reflection mode of reflecting a part of light. In the transflective type liquid crystal display device, an organic film which has uneven (concave or convex) patterns on its surface is coated over an insulating film so as to obtain good scattering characteristics. For example, after coating an organic film over on an insulating film by spin coating, depressed portions are patterned on the surface of the organic film by a photolithography process so as to form there uneven patterns.
This organic film is patterned into a predetermined shape within the display area, while the organic film outside the display area is conventionally formed without patterning over the surface. That is, the organic film is formed from the display area to the frame area which is outside of the sealing portion. Therefore, the organic film contacts the air at the outside of the sealing portion, and absorbs moisture as the time passes. Then, the moisture permeates into the panel through the organic film. This causes disorder of orientation of liquid crystal molecules when the liquid crystal display device is used for a long period of time, so that defective display easily occurs, thereby decreasing reliability.
As a method for solving such a problem, it is effective not to apply the organic film under the sealing portion. For example, in Japanese Unexamined Patent Application No. 2003-167258, there is disclosed a liquid crystal display device of a structure having no organic film under the sealing portion. In the Japanese Unexamined Patent Application No. 2003-167258, an opening is formed in the forming area of a sealing material. The opening penetrates an inorganic insulating film covering a thin film transistor (TFT) and an organic film layered over the inorganic insulating film, and reaches an interlayer insulating film applied between a source line and a gate line. Then, the sealing material is formed in this opening in order to bond opposing substrates. Since this structure makes the sealing material adhere not to the organic film but to the interlayer insulating film, thereby increasing the adhesion strength.
Moreover, according to the Japanese Unexamined Patent Application No. 2003-167258, at the display area side from the sealing portion, the connection of the source line is changed to a line formed of the same layer as that of the gate line, and then the source line is led to the outside of the sealing portion. Thus, since the source line is once changed to the same layer as that of the gate line, the upper part of a lead line underlying the sealing portion is protected by the interlayer insulating film. By virtue of this structure, it is possible to prevent the lead line of the source line from directly contacting the sealing material, thereby maintaining good resistance to corrosion.
However, the structure described in the Japanese Unexamined Patent Application No. 2003-167258 needs to be provided with a change unit for changing the source line to the lead line of the same layer as that of the gate line. Therefore, in the change unit, a contact hole is formed in the interlayer insulating film in order to connect the source line to the lead line in the same layer as that of the gate line. Thus, the step of forming the contact hole in the interlayer insulating film is newly needed, thereby increasing the number of manufacturing steps. Moreover, space for the change unit is also newly needed, thereby increasing the width of the frame area.
Moreover, according to the Japanese Unexamined Patent Application No. 2003-167258, at the process of forming the contact hole for connecting a drain electrode to a pixel electrode, an opening which penetrates the inorganic insulating film and the organic film is formed in the sealing portion. Specifically, after forming an inorganic insulating film which covers the TFT, a pattern of an organic film is formed thereon. Dry etching of the inorganic insulating film is performed using this pattern of the organic film as a mask. At this time, the interlayer insulating film under the inorganic insulating film is exposed to an etching gas at the opening. Thus, the interlayer insulating film may be damaged, thereby there is concern that insulation between the lead lines may be decreased. If the interlayer insulating film is further damaged, the lead line will be exposed to contact the sealing material directly, so that there is a possibility of the line being broken by corrosion. Thus, there is concern that the reliability may be reduced.
In addition, another method can be considered in which when forming the opening which penetrates the inorganic insulating film and the organic film in the sealing portion, patterning of the inorganic insulating film is performed first, and then, a pattern of the organic film is formed thereon in order to reduce the damage of the interlayer insulating film. However, according to this method, the inorganic insulating film is patterned separately, thereby increasing the number of the steps of photolithography by adding one step. Thus, there is a problem of causing an increase of the manufacturing cost and a lengthening of the manufacturing period.
The present invention has been contrived to solve the problem described above, and an object thereof is to provide a transflective type liquid crystal display device which can improve the reliability without increasing the number of photolithography steps, and to provide a manufacturing method thereof.